The known brazing sheets to be used in heat exchanger systems usually are a three layer system comprising an outer 4xxx alloy clad, a 3xxx core alloy and a 7xxx or 1xxx innerliner alloy. In this specific use the inside wall of the successive parts of the heat exchanger is in direct contact with the cooling fluid and, because of the temperature of the fluid and the flow conditions, a high corrosion resistance is required. It is well known to use a Zn containing innerliner to improve the corrosion resistance of these brazing sheets. Common innerliners are made of for example a 7072 alloy or a 3003 alloy with Zn. The Zn containing innerliners act as sacrificial anodes, forcing the corrosion to attack the inner surface of the heat exchanger in a lateral way instead of penetrating the layer by localized pitting or intergranular corrosion.
As will be appreciated, alloy designations and temper designations, except otherwise indicated, refer to the Aluminum Association designations in Aluminum Standards and Data and the Registration Records, all published by the US Aluminum Association.
All percentages are in weight percent, unless otherwise indicated.
The brazing sheet disclosed in EP-1351795 (published as WO 02/055256) has an inner liner with 1.3-1.5 wt % Zn and, among other elements<0.4 wt % Si and 0.05-0.4 wt % Cu. Also in WO 02/055256, a 2 or 3 layer sheet is disclosed with a core of a 3xxx alloy and an innerliner with, among other elements, 0.7-3.0 wt % Zn.
In JP-11293372 high corrosion resistance is disclosed for a system with a 2 or 3 layer system with a core consisting of among other elements, 0.3-1.1 wt % Si, clad on one or both sides with sacrificial anode material consisting of, among other elements, 1.5-8 wt % Zn with Fe and Si compounds regulated.
From EP-1391679 a sacrificial waterside liner to be used in a heat exchanger is known with 1.0-10.0 wt % Zn and, among other elements, 0.4-3.0 wt % Ni.